The invention relates to a plasma processor and particularly to such a processor consisting of a multiturn helical coil atop an adjustable dielectric ceiling for performing reactive ion etch and chemical vapor deposition.
Plasma-enhanced semiconductor processes for etching, deposition, resist stripped, passivation, or the like are well known. Generally, plasma may be produced from a low-pressure process gas by inducing an electron flow which ionizes individual gas molecules through the transfer of kinetic energy through individual electron-gas molecule collisions. Most commonly, the electrons are accelerated in an electric field, such as a radiofrequency (RF) electric field. Various structures have been developed to supply RF fields from devices outside of a vacuum chamber of a plasma processor to excite a gas therein to a plasma state. Inductively coupled plasma (ICP) caused by coil is one kind of the devices. ICP offer many processing advantages including high reactive species densities, thus providing high electron density plasma, high process rates, as well as low and controllable sheath voltage. To produce an RF inductively coupled plasma, the coil inductor is adjacent to the chamber. One conventional apparatus was described by Jacob et al. in U.S. Pat. No. 3,705,091, in which the plasma was generated inside a low pressure cylindrical vessel within the helical coil which energized by 13 MHz RF radiation. This apparatus not only has high etch rate performance, but also has serious contamination due to sputtering of the dielectric vessel walls caused by capacitive coupling created by the RF potentials on the coil with the vessel walls.
In U.S. Pat. No. 4,948,458, Ogle et al. disclose the plasma is generated at a low pressure such as 0.1 milliTorr to 5 Torr by using a spiral coil positioned on or adjacent to a planar dielectric called a window. The coil is responsive to an RF source having a frequency in the range of 1 to 100 MHz (typically 13.56 MHz), and is coupled to the RF source with an impedance matching network. According to the disclosure in U.S. Pat. No. 5,619,103, the extra dielectric acts as to reduce the effects of capacitive coupling between the coil and the plasma.
Cuomo et al. in U.S. Pat. No. 5,622,635 discloses a plasma chamber further comprises a conductive shield between a spiral coil or a helical coil and a planar dielectric window. The shield is designed to guide capacitive coupling generated by the coil away from the plasma-window interface.
More effective reduction of capacitive coupling and higher induction power may be attained by using a multiturn coil with the lower turn thereof grounded [Frogotson et al., entitled xe2x80x9cInductively Coupled Plasma for Polymer Etching of 200 mm Wafersxe2x80x9d, J. Vac. Sci. Technol. B 14(2), pp. 732-737, 1996]. However, as Frogotson et al. taught in this article that the matching network could not properly tune the larger self-inductance of a three-turn 24-cm-diam helical coil with 6 mm cross sectional diameter at the 13.56 MHz drive frequency.
Another problem should be considered in manufacturing plasma processor, that is the uniformity of reactive species such as oxygen ions or radicals in the plasma generation chamber. In some deposition conditions, the chamber pressure tends to be somewhat higher that reduce the mean free path of these reactive species, and results in a nonuniform plasma density due to recombination of the reactive species. One possible solution would be to raise the height of the dielectric ceiling and to increase the height of the coil antenna above the wafer treated. Another possible solution would be to operate the source region at a very low pressure (below 1 milliTorr). In U.S. Pat. No. 5,614,055, Fairbaim et al. discloses a dome-shaped plasma processor to improve the plasma generation uniformity of a oxygen gas via increasing the height of the coil antenna above the wafer treated. U.S. Pat. No. 5,556,521 discloses a sputter etching apparatus having a dome-shaped dielectric extending into the processing chamber toward a substrate, in which a contoured inductive coil is disposed on the dielectric so as to generate dense uniform plasma for an uniform etch rate at low pressure about 1 milliTorr. The contoured inductive coil used in ""521 is convex-shaped in the direction of the substrate and thus is somewhat difficult to be made. As a result, the plasma generation uniformity is adversely affected.
For achieving the goals of low capacitive coupling, high induction power density and high uniformity of reactive species needed by the industry as mentioned above, the present invention provides a multitum (turn number xe2x89xa74) coil atop an adjustable dielectric for exciting gases in an RF vacuum plasma processor.
The present invention discloses a plasma processor which includes a four-turn 30-cm-diam helical coil managed to match with an impedance at an RF source of 13.56 MHz. This apparatus of the present invention will reduce the capacitive coupling problem comparing to some similar plasma apparatus.
In accordance with another aspect of the present invention, the helical coil is put into a conformal can-like dielectric to prompt an RF plasma species more approaching the wafer surface at a low pressure (0.001 milliTorr to 10 milliTorr), thus providing higher power density and higher etch rate.
In accordance with further aspect of the present invention, a cap-like dielectric conformal to the helical coil is introduced into the processor. This modification is one skill to raise the dielectric ceiling above the wafer treated for improving the problem of plasma concentration in the chamber under deposition conditions.
An inductively coupled plasma processing chamber constructed in accordance with the present invention comprises a dielectric window having a planar base and an integrally formed upright wall surrounding the planar base.
The present invention also provides a method of increasing a flux of ionic species of an inductively coupled plasma generated under a vacuum pressure of 0.001 to 10.0 milliTorr in a vacuum chamber having a fixed upright height between a bottom plate and a ceiling thereof. The method comprises using a dielectric window, as a part of the ceiling, having a planar base and an integrally formed upright wall surrounding the planar base, when the inductively coupled plasma is generated, wherein the dielectric window is hermetically connected to the ceiling and so that the planar base of the dielectric window extends into the vacuum chamber.
The present invention further provides a method of increasing a plasma generation uniformity of an inductively coupled plasma generated under a vacuum pressure higher than 10.0 milliTorr in a vacuum chamber having a fixed upright height between a bottom plate and a ceiling thereof, which comprises using a dielectric window, as a part of the ceiling, having a planar base and an integrally formed upright wall surrounding the planar base wherein the dielectric window is hermetically connected to the ceiling and so that the planar base of the dielectric window protrudes from the vacuum chamber.
Preferably, the dielectric window is cylindrical.
Preferably, the upright wall has a height from the planar base less than 10 cm, more preferably less than 5 cm.
The inductively coupled plasma processing chamber of the present invention may further comprises a chamber body, in which a free end of the upright wall of the dielectric window is hermetically connected to the chamber body to provide a plasma generation space confined by the dielectric window and the chamber body. Preferably, the chamber body comprises a bottom plate, an upright side wall surrounding the bottom, and a flange at a free end of the upright side wall, wherein the flange extends inwardly from the upright side wall so as to form an aperture above the bottom plate, wherein the dielectric window hermetically seals the aperture. The dielectric window is hermetically connected to the chamber body so that the planar base of the dielectric window either protrudes from the chamber body or extends into the chamber body.
Preferably, a coil is disposed adjacent to the planar base of the dielectric window for bringing about an inductively coupled plasma. More preferably, the coil is a helical coil and the dielectric window is cylindrical, wherein the helical coil is coaxially disposed adjacent to the planar base of the dielectric window.
Further advantageous embodiments of the invention ensue from the features disclosed in the dependent claims.